<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>margin</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        div{
            height: 200px;
            width: 200px;
            background-color: #acf;
            margin: 40px;
        }
        .down{
            overflow: hidden;
        }
    </style>
</head>
<body>
    <div class="up"></div>
    <div class="down"></div>
</body>
</html>